1. Field of the Invention
The present invention relates to a resonator and filter, especially to the resonator and filter that can be used in a portable radiophone.
2. Description of the Prior Art
FIG. 33 is a perspective view showing a conventional resonator, and FIG. 34 is a sectional view taken on line XXXIV--XXXIV in FIG. 33, and FIG. 35 is an exploded perspective view showing a laminated body used for the resonator. A resonator 1 includes a laminated body 2 having a rectangular prism shape. The laminated body 2 includes a first dielectric layer 3a having a rectangular shape. A line electrode 4 having a loop shape is formed on one surface of the first dielectric layer 3a. The line electrode 4 is formed from one edge to the center portion of the dielectric layer 3a. The line electrode 4 acts as an inductor. A take-out electrode 5 is formed from the intermediate portion of the line electrode 4 to another edge of the first dielectric layer 3a, on one surface of the first dielectric layer 3a. A first earth electrode 6a is formed on the other surface of the first dielectric layer 3a. The first earth electrode 6a has four lead-out electrodes 7a which extend to two opposite ends of the other surface of the first dielectric layer 3a. On the other surface of the first earth electrode 6a, the first protection layer 8a made of dielectric or insulating material is formed so as to cover the first earth electrode 6a. A second dielectric layer 3b is formed on one surface of the first dielectric layer 3a so as to cover the line electrode 4 and the like. A second earth electrode 6b is formed on the second dielectric layer 3b. The second earth electrode 6b has four lead-out electrodes 7b which extend to the two opposite ends of the second dielectric layer 3b. A second protection layer 8b made of dielectric or insulating material is formed on the second dielectric layer 3b so as to cover the second earth electrode 6b.
Six external electrodes 9a-9f are formed on the side faces of the laminated body 2. The external electrode 9a is connected to one end of the line electrode 4 and to the lead-out electrodes 7a and 7b of the first and the second earth electrodes 6a and 6b. The external electrode 9a is used as an earth terminal. The external electrodes 9b, 9d and 9e are connected to the lead-out electrodes 7a and 7b of the first and the second earth electrodes 6a and 6b respectively. The external electrode 9f is connected to the take-out electrode 5 of the line electrode 4. The external electrode 9f is used as an input/output terminal.
FIG. 36 is a perspective view showing a conventional filter, and FIG. 37 is a sectional view of taken on line XXXVII--XXXVII in FIG. 36, and FIG. 38 is an exploded perspective view showing a laminated body used for the filter. A filter 11 includes a laminated body 12 having a rectangular prism shape. The laminated body 12 includes a first dielectric layer 13a having a rectangular shape. First and second line electrodes 14a and 14b having a loop shape are formed separately on one surface of the first dielectric layer 13a. The first and the second line electrodes 14a and 14b are formed symmetrically from opposite ends of the dielectric layer 13a to the center portion, on one main surface of the dielectric layer 13a. The first and the second line electrodes 14a and 14b are coupled electromagnetically. The first and the second line electrodes 14a and 14b act as inductors of resonators. First and second take-out electrodes 15a and 15b are formed respectively from the intermediate portions of the first and the second electrodes 14a and 14b to the two ends of the first dielectric layer 13a, on one surface of the first dielectric layer 13a. A first earth electrode 16a is formed on the other surface of the first dielectric layer 13a. The first earth electrode 16a has six lead-out electrodes 17a which extend to the edges of the other surface of the first dielectric layer 13a. On the other surface of the first earth electrode 16a, a first protection layer 18a made of dielectric or insulating material is formed so as to cover the first earth electrode 16a. A second dielectric layer 13b is formed on one surface of the first dielectric layer 13a so as to cover the first and second line electrodes 14a and 14b. A second earth electrode 16b is formed on the second dielectric layer 13b. The second earth electrode 16b has six lead-out electrodes 17b which extend to the edges of the second dielectric layer 13b. A second protection layer 18b made of dielectric or insulating material is formed on the second dielectric layer 13b so as to cover the second earth electrode 16b.
Eight external electrodes 19a-19h are formed on the side faces of the laminated body 12. The external electrode 19a is connected to one end of the first line electrode 14a, and to the lead-out electrodes 17a and 17b of the first and the second earth electrodes 16a and 16b. The external electrode 19c is connected to one end of the second line electrode 14b, and to the lead-out electrodes 17a and 17b of the first and the second earth electrodes 16a and 16b. The external electrodes 19a and 19c are used as earth terminals. The external electrodes 19b, 19e, 19f and 19g are connected to the lead-out electrodes 17a and 17b of the first and the second earth electrodes 16a and 16b respectively. The external electrode 19h is connected to the first take-out electrode 15a of the first line electrode 14a. The external electrode 19d is connected to the second take-out electrode 15b of the second line electrode 14b. The external electrodes 19h and 19d are used as input/output terminals.
In the resonator 1 shown in FIG. 33, the distance between the line electrode 4 and the first earth electrode 6a and the distance between the line electrode 4 and the second earth electrode 6b are required to be wide, for example, more than 600 .mu.m respectively, for obtaining a high Q value of about 60. This results in a large device size and a thick configuration.
In the resonator 1 shown in FIG. 33, the length of the line electrode 4 is required to be increased in order to increase the inductance component of the line electrode 4, in order to lower the resonance frequency. This also results in a large device size.
In the filter 11 shown in FIG. 36, the distance between the first and the second line electrodes 14a, 14b and the first earth electrode 16a and the distance between the first and the second line electrodes 14a, 14b and the second earth electrode 16b are required to be wide respectively, for obtaining a lower insertion loss with and a high Q value of each resonator. This results in a large device size and a thick configuration.
In the filter 11 shown in FIG. 36, the length of the first and the second line electrodes 14a and 14b are required to be increased in order to obtain a large inductance component of the first and the second line electrode 14a and 14b, in order to lower the resonance frequency of each resonator. This also results in a large device size.